The present invention relates to a method and a device for controlling a mechanical supercharger, positioned in the intake tract of an internal combustion engine, which is coupled to a drive via a controllable clutch, switching the supercharger on and off being done by a control signal acting upon an actuator of the clutch.
A method and a device for controlling such a mechanical supercharger are known, for example, from the non-prepublished German Patent Application No. 1 00 39 081.1 filed on Aug. 10, 2000. The crankshaft of the internal combustion engine is here used as the drive for the mechanical supercharger, and it may be coupled by force locking to the supercharger via the controllable clutch. The clutch is opened or closed by a control signal which is ascertained in an electronic control unit as a function of operating conditions, especially as a function of the load of the internal combustion engine, and in this manner the mechanical supercharger is coupled to the drive or decoupled from the drive.
It has been shown that freezing up of the supercharger can occur, at least in response to certain supercharger arrangements under certain operating conditions. In this connection, the frozen-up supercharger can lead to considerable reduction in the flow cross section for the intake air, so that, in the extreme case, starting the combustion engine is no longer possible.
By switching on the supercharger when the combustion engine is started, particularly before beginning fuel injection, it is possible to break loose a frozen-up mechanical supercharger. In the extreme case, this also ensures the start of the combustion engine.
It is particularly advantageous that the breaking loose of the supercharger occurs even before the actual speed runup of the combustion engine, so that the driver cannot feel it happening.
It is also advantageous that the supercharger is broken loose even before the beginning of fuel injection, so that the subsequent start of the combustion engine always takes place under the same boundary conditions, and is thereby applicable.
A particularly preferred implementation is that, when a predefined engine speed is exceeded, which leads to the inference that the starter is being operated (for example, 150 revolutions per minute), closing of the clutch takes place for a predetermined time, while when it falls below this speed threshold, possibly with the addition of a hysteresis quantity, opening of the clutch takes place immediately. It is particularly advantageous that this takes place only at low temperatures.
This procedure demonstrates especially advantageous effects with mechanical superchargers which are installed in the flow direction after the throttle, and have no air bypass.